The present invention relates to optical fibers coated with novel silicone compositions. More particularly, the present invention relates to optical fibers having a silicone cladding or protective coating thereon, said silicone composition comprising the reaction product of a silicone fluid, a silicone resin, and a reactive organic monomer such as an alpha olefin.
The emerging field of light wave telecommunications makes use of light to transmit information through a transparent medium in a way comparable to transmitting electricity through a copper wire. The advantage of such optical telecommunications over the presently employed electromagnetic systems is that it has the potential to accomodate thousands of times more communications traffic than radio communications.
Since the discovery of lasers the only technical obstacle to lightwave communications over great distances has been the development of a suitable transmission medium. Air, for example, although penetrable by light, is unsuitable because rain, fog and other atmospheric conditions can weaken the light signal. Development of the glass fiber lightguide, or optical fiber, provided an excellent and relatively inexpensive transmission medium.
Modern optical fibers typically consist of a core of high transparency silica glass which transmits the light surrounded by a protective or cladding layer. Such protective coatings not only insulate the optical fiber from the environment, but also act as an internal mirror reflecting the light back into the core, thus preventing loss of the light signal outside the optical path.
In the production of fiber optics cable for telecommunications, the material used as the protective layer must be very flexible, not adhere too closely to the glass fiber core, and maintain its integrity and optical characteristics in changing environments, including temperature cycles of from -50.degree. C. to 80.degree. C. It is also desirable that the protective layer be easily strippable so that the integrity of the fiber can readily be checked.
The prior art discloses various silicone compositions which are expressly said to be suitable as a coating composition for optical fibers, and silicone compositions which do not refer to their suitability for such use, typically because they were invented before the present optical fiber technology was developed.
Included in the first class is Suzuki, U.S. Pat. No. 4,380,367, which discloses a coating for optical fibers, comprising:
(a) 100 parts by weight of a vinyl group terminated methylphenylpolysiloxane having a viscosity at 25.degree. C. of 100 to 15,000 centipoise and with a methyl/phenyl molar ratio of from 1/1 to 10/1;
(b) an organohydrogenpolysiloxane selected from methylhydrogenpolysiloxanes having a viscosity at 25.degree. C. of from 0.7 to 5000 centipoise and containing at least three silicon-bonded hydrogen atoms per molecule, and methylphenylhydrogenpolysiloxanes having a viscosity at 25.degree. C. of 0.7 to 5000 centipoise and containing at least three silicon-bonded hydrogen atoms per molecule, with a methyl/phenyl molar ratio not smaller than 1/1, the amount of (b) being an amount which provides a molar ratio of silicon-bonded hydrogen atoms in (b) to silicon-bonded vinyl groups in (a) which ranges from 0.8/1 to 10/1; and
(c) 0.5 to 1000 ppm precious metal or precious metal containing hydrosilation catalyst, as precious metal based on the total amount of (a) and (b).
Included in the latter class is Dallavia, U.S. Pat. application Ser. No. 538,093, filed Oct. 3, 1983, now U.S, Pat. No. 4,526,953 and incorporated by reference into the present disclosure. Dallavia discloses curable silicone compositions particularly suitable as release coating compositions which comprise:
(a) an addition curable diorganopolysiloxane base polymer having up to about 20 percent by weight alkenyl functional groups and having a viscosity of from about 50 centipoise to about 100,000 centipoise at 25.degree. C.;
(b) an SiH-containing polysiloxane crosslinking agent having up to 100 percent by weight SiH-containing siloxy groups and having a viscosity in the range of 15 centipoise to 1000 centipoise at 25.degree. C.;
(c) an effective amount of precious metal or precious metal containing catalyst to promote an addition cure hydrosilation reaction between said base polymer and said crosslinking agent; and
(d) an amount of .alpha.-olefin or mixture .alpha.-olefins having up to about 30 carbon atoms effective to enhance said addition cure.
Nelson, U.S. Pat. No. 3,284,406, discloses a composition consisting essentially of:
(a) a polysiloxane of the formula ##STR1## where R and R.sup.1 are phenyl or methyl and at least 80 mol percent of the R.sup.1 groups are methyl, said polysiloxane having a viscosity of from 500 to 500,000 centipoise at 25.degree. C.;
(b) from 5 to 50 percent by weight based on the weight of (a) and (b) of a copolymer of SiO.sub.2 units, (CH.sub.3).sub.3 SiO.sub.0.5 units and (CH.sub.3).sub.2 (CH.sub.2 .dbd.CH)SiO.sub.0.5 units, wherein there is from 1.5 to 3.5 weight percent vinyl groups based on the weight of (b), and the ratio of (CH.sub.3).sub.2 (CH.sub.2 .dbd.CH)SiO.sub.0.5 units to SiO.sub.2 units is from 0.6:1 to 1:1;
(c) a compound compatible with (a) and (b) which is a siloxane containing from 0.1 to 1.7 percent by weight siliconbonded hydrogen atoms, the remaining valences of the silicon atoms in (c) being satisfied by methyl or phenyl radicals, there being at least three silicon-bonded hydrogen atoms per molecule, and the amount of (c) being such that there is from 0.75 mol of SiH per mol of vinyl radicals in (a) and (b); and
(d) a platinum catalyst.
Modic, U.S. Pat. No. 3,436,366, discloses a composition
(a) a vinyl chainstopped polysiloxane having a viscosity of from 50,000 to 750,000 centipoise at 25.degree. C.,
(b) an organopolysiloxane copolymer comprising trimethylsiloxane units, methylvinylsiloxane units and SiO.sub.2 units, where from about 2.5 to 10 mole percent of the silicon atoms contain silicon-bonded vinyl groups and where the ratio of trimethylsiloxane units to SiO.sub.2 units is from 0.5:1 to 1:1;
(c) a platinum catalyst and
(d) an organohydrogenpolysiloxane crosslinking agent.
It has now been discovered that protective coatings for optical fibers can be prepared from curable silicone compositions, comprising:
(a) a substantially linear olefinic group-containing polydiorganosiloxane;
(b) a resinous olefinic group-containing polysiloxane;
(c) a reactive organic monomer;
(d) an organohydrogenpolysiloxane crosslinking agent; and
(e) an effective amount of precious metal or precious metal containing hydrosilation catalyst.